Putting the icon in front of the text results in adjacent space characters appearing as a box with 0020 inside (representing U+0020, the space character). See the green module here:

The text resulting in this is ï‹› {usage}%
Yep install otf-font-awesome and uninstall the others package like ttf.
It's a issue with gtk
@0xdec Is your problem solved? :)
That fixed it, thank you! I was under the impression that ttf generally has better support in Linux, thanks for the heads up!
For me this did not appear after every icon.
Space error after the backlight icon but not after the wifi or sound icon.
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Yep install otf-font-awesome and uninstall the others package like ttf.
It's a issue with gtk